Topalan, E.; Ciftci, H.; DeMirci, H.

The human epidermal growth factor receptor 2 tyrosine kinase domain (HER2-TKD) plays a central role in signal transduction and is a significant therapeutic target in cancer. This study aimed to produce soluble recombinant HER2-TKD in Escherichia coli to enable structural studies for drug screening applications. The HER2-TKD gene was cloned into the pET28a(+) expression vector and expressed in E. coli. Initial expression led to the formation of inclusion bodies; thus, sarcosyl was used to solubilize the aggregated protein. Several induction durations were tested to optimize soluble expression. SDS-PAGE analysis was used to monitor expression and solubilization efficiency. The recombinant protein was purified using size-exclusion chromatography and reverse affinity chromatography to remove the SUMO tag. Crystallization trials were initiated using commercial screens to obtain diffraction-quality crystals. Soluble HER2-TKD was successfully obtained after optimization of induction and solubilization conditions. Crystallization efforts are ongoing to improve crystal quality for future structural analysis. These results provide a foundation for structure-based drug discovery studies targeting HER2.